Smithfield Foods Inc, the world's largest pork producer, said on Tuesday it will soon raise half of its hogs on feed that does not contain the additive ractopamine, a lean muscle promoting drug that has been banned in China and Russia.

Two Smithfield plants, which handle 43,000 hogs a day or about 10 percent of the U.S. industry, already are ractopamine-free, Chief Executive Larry Pope said at the BMO Capital Markets Farm to Market Conference in New York.

On June 1, the company will convert a third plant to be ractopamine free. When that happens "over 50 percent of our operations will have no ractopamine as part of their feed rations," Pope said.

China, the world's largest pork consumer and the third largest market for U.S. pork with sales of over $800 million last year, wants pork from the United States to be verified by a third party from March 1 to be free of ractopamine, an additive that promotes lean muscle growth.

Russia, which imported $550 million worth of U.S. beef, pork and turkey last year, has banned imports of meat from the United States due to the presence of the food additive.

Smithfield, which was not immediately available for additional comment, in February said it was in the final stages of converting its plant in Tar Heel, North Carolina, the world's largest pork-processing facility, to be ready to meet China's new requirement before the March 1 deadline.

Shares of Smithfield closed up 87 cents, or 3.36 percent, on Tuesday at $26.80 at the New York Stock Exchange